An interview on PC Gamer with Marcin Iwinski is a conversation where the CD Projekt CEO comments on piracy, saying now matter how many times The Witcher 2 was pirated (which they estimate may have been as often as 4.5 million times), the game's lack of DRM was still the right call:

From the very beginning our main competitors on the market were pirates. The question was really not if company x or y had better marketing or better releases, but more like “How can we convince gamers to go and buy the legit version and not to go to a local street vendor and buy a pirated one?” We of course experimented with all available DRM/copy protection, but frankly nothing worked. Whatever we used was cracked within a day or two, massively copied and immediately available on the streets for a fraction of our price.

We did not give up, but came up with new strategy: we started offering high value with the product – like enhancing the game with additional collectors’ items like soundtracks, making-of DVDs, books, walkthroughs, etc. This, together with a long process of educating local gamers about why it makes sense to actually buy games legally, worked. And today, we have a reasonably healthy games market.

In any case, I am not saying that we have eliminated piracy or there is not piracy in the case of TW2. There is, and TW2 was [illegally] downloaded by tens of thousands of people during the first two weeks after release. Still, DRM does not work and however you would protect it, it will be cracked in no time. Plus, the DRM itself is a pain for your legal gamers – this group of honest people, who decided that your game was worth the 50 USD or Euro and went and bought it. Why would you want to make their lives more difficult?